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Release Notes: LLVM FOR RENESAS RL78 10.0.0.202303
Release Notes: LLVM FOR RENESAS RL78 10.0.0.202303
31st of March, 2023
CyberThor Studios Ltd. is releasing the LLVM for Renesas RL78 10.0.0.202303, a cross compiler tool for
Renesas RL78 micro-controllers.

SALIENT FEATURES
The LLVM for Renesas RL78 10.0.0.202303 toolchain is based on:❖ LLVM 10.0.0 [released]❖ Compiler-rt 10.0.0 [released]❖ Libcxx 10.0.0 [released]❖ Libcxx-abi 10.0.0 [released]❖ Newlib 4.1.0 [released]❖ GDB 7.8.2 [released]
LLVM RL78 comes with significant performance improvements (both code size and speed) compared to GCC
RL78. It also comes with support for latest language standards: full support for C17 and C++17 andexperimental support for the C2x (next C standard) and partial support for C++20.
The latest patches are applied to the LLVM sources.

ABOUT LLVM FOR RENESAS RL78 10.0.0.202303
Release Version:

LLVM for Renesas RL78 10.0.0.202303

Release Date:

31st of March, 2023
Ubuntu 18.04 or later (or compatible distribution)

Platforms Supported:
Windows 7 or later
Language:

C, C++

Targets:

G23, G1X, I1X, D1X, LIN MCP, F1X, and L1X

Object File Format:

ELF

CHANGES IN LLVM FOR RENESAS RL78 10.0.0.202303
This toolchain is the successor of GCC RL78 toolchain and it is meant as a direct replacement to GCC RL78.
This section describes the fixes made in the LLVM for Renesas RL78 10.0.0.202303 release.

1. [Improvement] Various codegen and runtime optimizations
Code speed and size optimizations were made in the compiler and runtime library.
2. [Improvement] Outlining of functions in user defined sections
A new mllvm option was added to instruct the compiler to take into account the function section names
when outlining functions.
Ex:void Func1() __attribute__((section(“SEC1”)));
void Func2() __attribute__((section(“SEC1”)));
void Func3();
Using -mllvm -use-section-attribute-in-outlined-functions will result in Func1 andFunc2 being considered for common code outlining.
Func3 will not be considered since it is in a different section.
3. [Bug fix] Wrong PLT usage in case of __far functions
A PLT entry was created even for __far functions, resulting in bad code being generated.
This was fixed in the current release.

Notes:
This installer does not provide an option to integrate the LLVM RL78 toolchain with e2 studio, as the e2studio IDE will automatically detect the LLVM RL78 toolchain installation on start-up for integration.
Alternatively, you may use the 'Toolchain Management' feature in e2 studio to achieve this.
For details on e2 studio please visit the following link below:
https://www.renesas.com/eu/en/software-tool/e-studio
There is no support in this installer to integrate the toolchain with the HEW IDE.

KNOWN ISSUES IN LLVM FOR RENESAS RL78 10.0.0.202303
The following is a list of known issues for the tools we include for the LLVM for Renesas RL78 10.0.0.202303
toolchain:
1. Assembly parsing issue of callt instruction operand.
The assembly parser cannot handle any complex expressions as operands for callt instruction, only constantvalues are allowed at the moment.
2. Missing assembly listing support (-a[cdhlns] option in GNU AS).
There’s no equivalent in the LLVM for the -a[cdhlns] GNU AS option.
The alternative solution is to use llvm-objdump to obtain source code interleaved with assembly (-S,--source option).
3. Binding of references to packed fields.
Creating references to struct members which are declared as packed, e.q. __attribute__ ((packed)), isincorrect as it can cause unaligned access issues. The compiler should return an error in this case however
this is not currently the case. This will be fixed in a future release.
4. Inline assembly missing constraints and modifiers support for parameters.
Clang supports, in the case of RL78, inline assembly constructs without parameters, e.q. asm(AssembleTemplate).
The extended syntax available in GCC, asm (AssemblerTemplate : OutputOperands : InputOperands :Clobbers : GotoLabels), is not currently supported. This will be fixed in the next release, however theconstraints will not be the same as in GCC.
5. Far address space handling in C++ code
Currently far data, far rom and far code handling in C++ are not supported.
6. Newlib format specifiers
The pre-built newlib library included with the toolchain is built without using the-enable-newlib-io-c99-formats configure flag.
Without this flag, handling for some format specifiers will not be included in the resulting library.
Using libgen, users can build their own newlib, specifying the -D_WANT_IO_C99_FORMATS=1 option toinclude the extra format specifiers, at the cost of code size.

7. PLT usage for function calls over 64K
For each near call, where the callee was allocated over the 0xFFFF boundary, the linker will create an entryfor the callee (if it doesn't exist yet) in the Procedure Linkage Table(PLT).
The entry will consist of a BR !!<Callee> instruction and the address written to the call instruction will be
the address of the PLT entry.
This indirection allows developers to increase the address range they can allocate their code, without theusage of _far functions.
Example:test.c:void bar() __attribute__((section(".far_section")));
void foo() {bar();}linkerscript.ld:...
.far_section 0x111D8 : AT(0x111D8){. = ALIGN(2);*(.far_section). = ALIGN(2);} >ROM...
will result in the following ELF file:...
000000d8 .lowtext:
d8: ec d8 11 01...
00003004 _foo:
3004: fd d8 00
3007: d7...
000111d8 _bar:

br !!_bar
call !.lowtext
ret

8. Other issues, non-specific to RL78
LLVM tries to be a complete replacement. As such there are still a couple of missing features from GCC
which will be implemented in future releases. In particular, the following issues should be noted:
lld: Information printed using --print-gc-sections is not as nice as when using the GNU ld. Bug 46783
llvm-ar: Errors when printing multiple members with the same name. Bug 42521

llvm-dwarfdump: Does not print section attribute flags yet. Bug 38488
llvm-nm: Unable to understand symbols built with gcc-lto Bug 41437
llvm-nm: Needs support for --line-numbers to llvm-nm Bug 40001
llvm-objcopy: Unknown argument '--change-section-address'. Bug 45217
llvm-objcopy: Objcopy zero-size section might cause huge binaries. Bug 46299
llvm-objdump: Prints wrong line number info for obj file compiled with -ffunction-sections. Bug 40703
llvm-objdump: Wrong behavior for non-relocatable objects when suing llvm-objdump with -r option. BugBug 41901
llvm-readobj: Make GNU style symbol printing invalid symbol section indexes match GNU readelf Bug
43850
llvm-readelf: Relocation addends printed style does not match GNU readelf Bug 45235
llvm-string: Short option with argument grouping not GNU compatible Bug 42942
llvm-string: Allow "-<integer>" as an alias for "-n <integer>" Bug 42964
llvm-symbolizer: Shows incorrect source line info if --gc-sections used Bug 41124
llvm-symbolizer: llvm-addr2line does not exit when passed a non-existent file Bug 42754

9. Other issues
Finally, for better understanding regarding the status of the toolchain please visit https://bugs.llvm.org/ .
In particular, the following queries will help better understand the status of each tool.
https://bugs.llvm.org/buglist.cgi?bug_status=UNCONFIRMED&bug_status=NEW&bug_status=CONFIRMED&bug_status=REOPENED&component=ELF&product=lld&query_format=advanced&resolution=--https://bugs.llvm.org/buglist.cgi?bug_status=UNCONFIRMED&bug_status=NEW&bug_status=CONFIRMED&bug_status=REOPENED&component=llvm-ar&product=tools&query_format=advanced&resolution=--https://bugs.llvm.org/buglist.cgi?bug_status=UNCONFIRMED&bug_status=NEW&bug_status=CONFIRMED&bug_status=REOPENED&component=llvm-dwarfdump&product=tools&query_format=advanced&resoluti
on=--https://bugs.llvm.org/buglist.cgi?bug_status=UNCONFIRMED&bug_status=NEW&bug_status=CONFIRMED&bug_status=REOPENED&component=llvm-nm&product=tools&query_format=advanced&resolution=--https://bugs.llvm.org/buglist.cgi?bug_status=UNCONFIRMED&bug_status=NEW&bug_status=CONFIRMED&bug_status=REOPENED&component=llvm-objcopy%2Fstrip&product=tools&query_format=advanced&res
olution=--https://bugs.llvm.org/buglist.cgi?bug_status=UNCONFIRMED&bug_status=NEW&bug_status=CONFIRMED&bug_status=REOPENED&component=llvm-objdump&product=tools&query_format=advanced&resolution=--https://bugs.llvm.org/buglist.cgi?bug_status=UNCONFIRMED&bug_status=NEW&bug_status=CONFIRMED&bug_status=REOPENED&component=llvm-readobj&product=tools&query_format=advanced&resolution=--https://bugs.llvm.org/buglist.cgi?bug_status=UNCONFIRMED&bug_status=NEW&bug_status=CONFIRMED&bug_status=REOPENED&component=llvm-size&product=tools&query_format=advanced&resolution=--https://bugs.llvm.org/buglist.cgi?bug_status=NEW&bug_status=CONFIRMED&bug_status=REOPENED&com
ponent=llvm-symbolizer&product=tools&query_format=advanced&resolution=---

FREE SUPPORT FOR LLVM FOR RENESAS RL78 10.0.0.202303
For free technical support, please register athttps://llvm-gcc-renesas.com
For your feedback and suggestions, please visit
https://llvm-gcc-renesas.com/help/contact-us/